It has been known for almost two decades that poly(alkylene carbonates) of relatively high molecular weight are useful in the manufacture of fibers, films, coatings, and molding compounds, and can be prepared by the copolymerization of epoxides with carbon dioxide using an organometal catalyst. This process, however, has not yet reached full commercial production, in part because of the costs involved relating to yield, which in turn is dependent upon catalyst activity, including the loss of activity of the catalyst during polymerization.
U.S. Pat. No. 3,585,168 to Inoue, et al. (1971) discloses copolymerizing epoxides and carbon dioxide using an organometallic catalyst, such as diethyl zinc, with a cocatalyst having an active hydrogen, such as water, alcohol or ketone. Epoxides disclosed include propylene oxide, ethylene oxide, styrene oxide, isobutylene oxide and epichlorohydrin. The polycarbonates formed have substantially equal molecular ratios of carbon dioxide and epoxide and have molecular weights on the order of 10,000 to 200.000.
U.S. Pat. No. 3,900,424, Inoue, et al. (1975) describes how to improve an organometal catalyst for copolymerizing carbon dioxide and epoxy compounds by pretreating the catalyst with carbon dioxide. Neither the '168 nor the '424 patents, however, deal with the problem of reusing the catalyst in subsequent polymerization reactions.
Japanese patent disclosure 1977-(Sho 52)-151,116. Inoue, et al. (1977) describes metal carboxylates which are useful as catalysts in the homopolymerization of epoxides or copolymerization of epoxides with carbon dioxide. These catalysts contain di-, tri- or tetravalent metals or Group VIII transition metals as salts of both dicarboxylic and monocarboxylic acids, with at least two monocarboxylate groups in terminal positions in the molecule of the catalyst compound. Following polymerization, monocarboxylic acid can be added to aid in separating the catalyst for reuse. Any residual free carboxylic acid in the catalyst is said to inhibit polymerization activity.
Inoue and Yamazaki, Organic and Bio-Organic Chemistry of Carbon Dioxide pages 167-176, John Wiley & Sons New York (1982) discusses the copolymerization of carbon dioxide with epoxides and surveys several effective catalyst systems, including combinations of diethyl zinc with an aromatic dicarboxylic acid, but does not deal with the problems of recovering and reactivating spent catalyst.